Gosh, Bob Stuart! (Hey Bob)
I noticed the picture above your shoulder and looked closer to see that it is the X-4!!! Simply, you are the man. Your work on this was/is a game changer of quantum scale. I used your engineering thoughts so many times on the versions that I have been through. Don't know if you remember or are aware of the 3VG that Mother Earth News did back in the earlier 80's, but it and the X-4 have been the only two real points of reference I have used in my clean sheet of paper approach. Your understanding of physics as they relate to motion is unmatched...my hat is off :-) Do you know Craig Vetter? How about Ned Ryan Doyle? They both would like you :-)
Thanks for noticing the weight... Like the X-4, it was a huge obstacle, and at 350, I am not willing to take it any further for safety on the highway (First version Geek was over 500..and it took 6 years and 200k to get it to 3ish safely.)
(If you would like help on FB or anything, just PM me, and I will help you in any way I can.) (Listserv, hehehe..I hear you!)
On Cg and stability at speed, it' rides pretty well up to 70..when the slotted-center tires sling out to a 1/4" contact patch or so. I run her high, like you did, to counteract the crosswinds, and have had 30-40 mph cross and HW's at 65 plus thus far with reasonable control (40 mph hw at 70 lifted the nose 12" once early on..and I didn't poop for days after). We were running about 33% on each wheel with the 125, but I recon that the 250 is going to shift Cg a few inches aft. You are dead on with the wheel pants, too...they are like vertical wings with about 15lbs of force at 60, against a total 1/2" of tire patch combined. We are running bout 1 deg down on the front a-arms, for about 10-15 lbs downforce...and may increase it or add a spoiler to allow for wheel pants soon. I figured that we should be able to pop 150 or so first, then start with more DF until mpg falls off...and tweak.
One of the crazy things that you might dig is the relative effect that I found on aerodynamics (and maybe Darin did, too)... Being so clean on the body (Releasing at around 75% of tail zero), I can feel the pressure wave from passing cars...the sucking and "push"(Not normal buffeting). Dump truck and log-carrying 18 wheelers are holy hell...creating such a vortex/pressure wave that it will actually lift the body off the ground...like skipping on water. Not fun at all, and convinced me to add much weight to the front on retail versions.
before I went to dual a arms, I did a lot of research around your cantilever inboard design...eventually settling for the simplified versions, but I did test and see how amazing it is to bring the pivot axis substantially inboard!!
Gosh...again with caster and CP, you are a God... We are running about 4 deg pos right now, and everything we change is relative to "at speed" as you advised...using pressure to dictate angle...cause it changes like the dickens at aero levels. We can go as far as 7 pos, I think, but am waiting to settle her down a little before changing (Had 1 deg neg camber on both sides last run for centering test, going to -1 on right only next run, and zero toe.
I am hoping to get some serious mpg numbers in during the coming weeks...and then shut down for a bit to relocate to a bigger shop. After these two are done, I am going to focus on the fun stuff like you mentioned, roll resistance, lift, etc. We bought a Innovate LMA-3 and data recorder, and will be enjoying the benefits of the accelerometer then :-)
The back wheel was just set up for example, we are putting another spoker back there next week (With aero discs at some point). That Ninja wheel was heavy as the dickens!! (About 40 lbs!)
On canopy... our mad scientist team member, Kenneth, calls the clear canopy "The brain cooker"..and it does. We are working on a roof now, similar to the old gtp stuff...and the Oldsmobile aerotech. We will be piping exhaust heat for defrost in the new dash...and will probably do some work on the windshield angle soon. I really want to get to glass on the front, but you know how costly that is...we'll get there. Probably just raising the angle for now.. Wipers...ugh...and other joy. The plastic windshield does a pretty good job in mild rain, but I have found that turbulence/tight flow is an asset here (Initial "nose"pressure wave/dispersion is decreasing flow adhesion to the glass, lifting the air about 1/2", and not creating turbulence (Low pressure)...might put in a spoiler or experiment with pressurized air here..
We are running 18" all around, 3" front and 1.75 rear", Built by Buchanan's in Ca, and installed on 20mm hubs. We run WF920's 3" all around for the weight and RR for now.
Yes, it is a shame that the eco competition tires are not more readily available, or the VW XL1 tires, or the new BMW I3 tires, at reasonable prices. I am reading that EU is forging ahead with large diameter low resistance tires, but they are talking about not letting them out on the market till 2021! I have been doing a lot of reading on the skinny spares (17-18"), and may well look at using them on test stuff...delamination is my only concern, and only at significant velocity..
I would certainly step up to any effort that increases availability of above-par resources to this arena..and will make this a part of my public speak in the meanwhile..
Thank you so much for your fascinating thoughts, know that I will re-read and soak the message further.
Honored,
Ray
Quote:
Originally Posted by Bicycle Bob
Thanks for posting, Ray. Kudos on going lightweight. I don't go to Facebook for anything, since they pretty much destroyed the functioning listservs without replacing their usefulness. As far as I can tell, nothing I posted there was ever seen, probably because I had not done whatever it takes to target my ads.
With the rear engine, I think you will have problems with crosswind stability, and they will get far worse if you add fairings to the front wheels. Those are currently adding about 50% to the drag. Beware of the fairings being unstable themselves, as the most obvious shape puts the CP ahead of the kingpin axis. If you have to, you can just offset the kingpins and spindles to get trail for both steering and aero instead of using a caster angle. It works fine.
You really need to do a coast-down test, and find out what your power requirements are. Timing several points lets you separate out rolling and aero drag. It would also be nice to get the weight distribution and CG height, which can be calculated by weighing the front and rear with each end lifted in turn.
There is a great account of the test results on a WWII fighter aircraft, from the original shape to one with cooling vents, guns, and other little details. The drag doubled. The devil is in the details, covering all spokes and managing the flow in shear between moving and stationary parts, minimizing or fully sealing openings, gently ducting and closely regulating the cooling air, etc. Laminar flow is very seldom present on road vehicles, as the slightest blemish or irregularity trips it to regular turbulent flow, spreading out at 30 deg from there back. The back wheel looks nice, but expensive on fuel.
The windshield/roof will bake you on a sunny day, and the angle somewhat impairs vision, especially if there are any manufacturing defects. It will need a defroster, being hard to reach, and an outside wiper that won't scratch it with road grit.
If you are using 17" wheels, you might be able to pry loose a set of Michelin solar race car tires, which would probably halve your rolling drag. Maybe we should set up some sort of petition or PR campaign to make those generally available.
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